1. Field of the Invention
The invention relates to dispensing materials from a container using apparatus including a follower plate assembly which is lowered into the container housing the material to be dispensed. The follower plate assembly includes a base plate which is heated to melt the material and a separate cylindrical member which includes sealing means for use in preventing leakage of such material at the interface of the base plate and the inner wall or surface of the container as the follower plate assembly is being lowered into the container in a known manner. Sealing means are also provided which prevent leakage between the interface of the base plate and separate cylindrical member while facilitating expansion of the base plate relative to the cylindrical member and preventing undesirable heat transfer to the cylindrical member as the temperature of the base plate is increased during operation of the follower plate assembly.
2. Description of the Prior Art
The viscosity of materials to be dispensed using apparatus of the present invention varies depending upon the specific application, and it is not unusual to find materials which are not particularly viscous and are substantially free flowing. On the other hand in certain applications such materials may be viscous to the extent to require the application of heat and/or pressure in order to render such materials dispensable. The present invention is applicable to apparatus for dispensing those materials which require the use of heat and pressure for adequate dispensing.
In one form of apparatus of the type contemplated by the present invention a plate is caused to reciprocate into and out of the open end of a drum-like container housing the material to be dispensed. Examples of such a plate are disclosed in Moore, U.S. Pat. Nos. 4,270,674 and 4,344,547. In operation, as the plate enters the drum it engages the inside surface of the drum and the material therein. As the plate travels towards the closed base of the drum it causes the material sandwiched or pressured therebetween to be dispensed, as for example, by forcing the material through an opening in the plate. Such dispensing may be facilitated by means of a pump associated with such opening to pump the material therethrough as the plate is lowered into the drum. The dispensing operation is further facilitated by applying heat to the material within the drum. This may be accomplished by, for example, utilizing a plate which includes a heating element affixed thereto or disposed internal thereof. The dispensing of highly viscous material usually requires the combination of such heat, pressure and pumping action to adequately dispense the material. Examples of a dispensing apparatus which may rely upon heat, pressure and pumping are disclosed in Moore, U.S. Pat. Nos. 3,982,699 and 4,355,734.
As the plate is lowered into the drum and engages the material, there is a tendency for the material to flow from the bottom of the plate over the top of the plate at the peripheral surface or edge thereof where the plate is adjacent to the inside surface of the drum. For example, in those instances where the plate is cylindrical and is caused to extend into a cylindrical drum for purposes of dispensing material from within the drum, there is a tendency for the material to flow or leak between the outer periphery of the cylindrical plate and the inside surface of the drum. In order to prevent such leakage and to direct substantially all of the material through the dispensing opening in the plate, sealing means or wipers have been used. For example, the cylindrical plate discussed above may be encircled with one of more resilient sealing means which serve to scrape the inside surface of the drum and also to prevent or reduce leakage at the interface between the inside surface of the drum and the periphery of the plate. Such wipers generally are O-ring-like resilient seals, either solid or inflated, which are fastened to the end of the plate and caused to seat in an associated groove which extends about the peripheral surface of the plate. Examples of such wipers are disclosed in U.S. Pat. Nos. 3,282,469; 3,412,903; 3,637,111; 3,758,003; 3,976,229; 4,073,409; 4,227,069; 4,195,755; 4,240,567; 4,534,493; 4,592,491; 4,635,820; and, 4,661,688.
In operation of such apparatus the follower plate is heated to as high as 500 degrees F. or more in order to melt the material to be dispensed. As the temperature of the follower plate is increased there is a tendency for it to expand. Such expansion tends to press the resilient seals against the inside wall of the container from which material is being dispensed. The result is that the seals tend to abrade or otherwise prematurely fail. In addition, there is a tendency for the follower plate to be bound within the container. When using a fiber drum, fiber drum liner or the like there is also the tendency for such expansion to damage the liner or drum. In addition, seals which are coupled directly to the follower plate are subjected to thermal degradation resulting from such high temperatures. Although it is desirable that the seals which engage the inside wall of the container and the material adhering thereto reach a temperature adequate to prevent the material from solidifying in the vicinity of such seals, it is undesirable for the seals to reach the excessive temperatures reached by the follower plate per se. It is possible to mount the seals upon a member which is separate from but coupled to the follower plate. However, heat transfer from the follower plate to such separate member will still cause thermal degradation of the seals. In addition, as the temperature of such separate member increases, it will expand causing the same problems discussed above caused by forcing the seals against the inside wall of the container as the follower plate per se expands. Further, when melting highly viscous material, it is often desirable to cause the follower plate to bear against the surface of the material with a great degree of pressure to facilitate dispensing. In those instances where the seals are attached to a separate member there will be a tendency for the molten material to leak at the interface between such separate member and the follower plate due to the combination of high pressure and high temperature to which the material is subjected. Such leakage may cause the molten material to flow into the area above the follower plate where electrical components used in the heating of the follower plate are housed. Such leakage is obviously undesirable. Leakage could be reduced, if not eliminated, by reducing the pressure exerted by the follower plate against the material to be dispensed. However, this will reduce the rate of flow of the material during the dispensing operation. In addition, the interface between the follower plate and separate member will tend to provide a path for oxygen to pass into the container thereby exposing the material to undesirable oxidation. Any attempt to seal the interface must deal with temperatures as high as 500 degrees F. or more, pressures of the material being dispensed of up to 100 pounds per square inch or more, and the expansion of the follower plate. This presents a dilemma in that such high temperature and expansion of the follower plate will tend to degrade elastomeric seals. On the other hand, a metal-to-metal seal might require pressure between the separate member and the follower plate in the order of magnitude of up to 3000 pounds per square inch or more. Such excessive pressure will impede movement of the follower plate relative to the separate member during thermal expansion of the follower plate.
It is highly desirable to provide a follower plate assembly wherein expansion of a heating plate as temperature of the plate increases does not cause damages to the resilient wipers.
It is also desirable to provide a follower plate assembly wherein expansion of a heating plate as temperature of the plate increases does not damage the drum or drum liner from which material is to be dispensed.
It is desirable to provide a follower plate assembly wherein expansion of a heating plate as temperature of the plate increases does not cause the assembly to become bound within the container from which material is to be dispensed.
It is further desirable to provide a follower plate assembly wherein increasing the temperature of a heating plate does not damage the resilient wipers of the assembly.
It is further desirable to provide a follower plate assembly wherein increasing the temperature of a heating plate provides adequate heat transfer to heat the resilient wipers of the assembly to an extent to prevent the material being melted from solidifying in the vicinity of the wipers without thermal degradation of the wipers.
It is also desirable to provide a follower plate assembly including a heating plate and separate member for carrying the wiper(s) wherein the material to be melted can be subjected to high pressure and temperature without substantial leakage at the heating plate-separate member interface.
It is further desirable to provide a follower plate assembly including a heating plate and separate member for carrying the wiper(s) wherein the material to be melted can be subjected to high pressure and temperature without leakage of oxygen into the container from which material is being dispensed.
It is further desirable to provide a follower plate assembly including a heating plate and separate member for carrying the wiper(s) wherein the material to be melted can be subjected to high pressure and temperature without impeding movement of the heating plate, caused by thermal expansion of the heating plate, relative to the separate member.